Why does my lake disappear when I deactivate AFFECTS LANDSCAPE?

I have this small lake (oasis), and I would use it without influencing the landscape, as you can see it pops up ugly.

However, deactivating AFFECTS LANDSCAPE, only makes it disappear.

Any idea of what could be wrong?

I checked and rechecked and the lake level is well over the surface, as you can see.
Is there any particular consideration to place lakes without affecting the landscape?

Also: it seems that the lake is not part of my landscape.
I built a layer for it, but apparently it fell off the layers and it’s an independent entity:


As you can see, there are no entities in the Lake layer, and yet it’s affecting the landscape.
Is this ok?